glsl/linker: Make update_array_sizes apply to just uniforms.

Commit 586b4b5 (glsl: Also update implicit sizes of varyings at link
time) extended update_array_sizes() to apply to both uniforms and
shader ins/outs.  However, doing creates problems for geometry
shaders, because update_array_sizes() assumes that variables with
matching names in different parts of the pipeline should have the same
sizes.  With the addition of geometry shaders, this is no longer true
(e.g. both vertex and geometry shaders have a gl_ClipDistance output
variable, but there's no reason these variables should have the same
sizes).

The original reason for commit 586b4b5 (avoid problems with
gl_TexCoord being 0 length) has since been addressed by commit 6f53921
(linker: Ensure that unsized arrays have a size after linking).  So go
ahead and switch update_array_sizes() back to only acting on uniforms.
!UPSTREAM: glsl: Enable various extensions for geometry shaders.

Note: In principle there's no reason geometry shaders couldn't support
OES_texture_3D and OES_EGL_image_external, but it seems silly to
enable them, since these are GLSL ES extensions, and geometry shaders
aren't allowed in GLSL ES.

TODO:
- Better commit message
- Better testing
main: Fix geometry shader error messages (missing right paren)
!UPSTREAM ===== BEGIN rebase of Plombo's GS patches =====
draw/gs: fix allocation of buffer for GS output vertices

Before, it accounted for the size of the vertices but not the other fields
in the vertex_header struct, which caused memory corruption.
mesa: add EXT_geometry_shader4 and ARB_geometry_shader4 to extension list
mesa: account for geometry shader texture fetches in update_texture_state
glcpp: define extension macros for EXT/ARB_geometry_shader4
glsl: add builtins for EXT/ARB_geometry_shader4

v2 (Paul Berry <stereotype441@gmail.com>): Account for rework of
builtin_variables.cpp.  Allow GL_{ARB,EXT}_geometry_shader4 extension
to be specified in fragment shaders, so that the gl_PrimitiveID
fragment shader input is accessible.  Use INTERP_QUALIFIER_FLAT for
gl_PrimitiveID so that it will obey provoking vertex conventions.
glsl: add ir_emitvertex and ir_endprim instruction types

These correspond to the EmitVertex and EndPrimitive functions in GLSL.

v2 (Paul Berry <stereotype441@gmail.com>): Add stub implementations of
new pure visitor functions to i965's vec4_visitor and fs_visitor
classes.
glsl: lower gl_ClipDistanceIn to gl_ClipDistanceInMESA in lower_clip_distance

This corresponds to the lowering of gl_ClipDistance to gl_ClipDistanceMESA.
It converts the 2D array gl_ClipDistanceIn from EXT/ARB_geometry_shader4 to
a 1D array of vec4s, gl_ClipDistanceInMESA.

v2 (Paul Berry <stereotype441@gmail.com>): Fix indexing order for
gl_ClipDistanceIn lowering.  Properly lower bulk assignment of
gl_ClipDistanceIn[i].
glsl: support compilation of geometry shaders via EXT/ARB_geometry_shader4

This commit adds all of the parsing and semantics for EXT/ARB_geometry_shader4,
including support for 2D arrays as inputs.

v2 (Paul Berry <stereotype441@gmail.com>): Adjust i965's
brw_link_shader() to pass the new is_geometry_shader argument to
do_set_program_inouts.  Add a few missing calls to
get_pipeline_stage().  Fix some signed/unsigned comparison warnings.
Fix handling of NULL consumer in assign_varying_locations().

v3 (Bryan Cain <bryancain3@gmail.com>): fix indexing order of 2D
arrays.  Also, allow interpolation qualifiers in geometry shaders.

v4 (Paul Berry <stereotype441@gmail.com>): Eliminate
get_pipeline_stage()--it is no longer needed thanks to 030ca23 (mesa:
renumber shader indices according to their placement in pipeline).
mesa: Refactor copying of linked program data.

This patch creates a single function to copy the the UsesClipDistance
flag from gl_shader_program.Vert to gl_vertex_program.  Previously
this logic was duplicated in the i965-specific function
brw_link_shader() and the core mesa function _mesa_ir_link_shader().

This logic will have to be expanded to support geometry shaders, and I
don't want to have to update it in two separate places.
mesa: Copy linked program data for GS.

The documentation for gl_shader_program.Geom and gl_geometry_program
says that the former is copied to the latter at link time, but this
wasn't happening.  This patch causes _mesa_ir_link_shader() to perform
the copy, and updates comment accordingly.
glsl: Require geometry shader inputs to be arrays.
glsl/linker: Properly error check VS-GS linkage.

From the ARB_geometry_shader4 specification:

    A geometry shader may also read from an input varying variable declared
    with the "varying in" qualifiers. The value read will be the same value as
    written by the vertex shader for that varying variable. Since a geometry
    shader operates on primitives, each input varying variable needs to be
    declared as an array. Each element of such an array corresponds to a
    vertex of the primitive being processed. If the varying variable is
    declared as a scalar or matrix in the vertex shader, it will be a
    one-dimensional array in the geometry shader.

Therefore, a user-defined geometry shader input will always be an
array, and the *element type* of that array should match the type of
the corresponding vertex shader output.
glsl/linker: Properly pack GS input varyings.

Since geometry shader inputs are arrays (where the array index
indicates which vertex is being examined), varying packing needs to
treat them differently.
glsl: Modify varying packing to use a temporary exec_list.

This patch modifies lower_packed_varyings to store the packing code it
generates in a temporary exec_list, and then splice that list into the
shader's main() function when it's done.  This paves the way for
supporting geometry shader outputs, where we'll have to splice a clone
of the packing code before every call to EmitVertex().

As a side benefit, varying packing code is now emitted in the same
order for inputs and outputs; this should make debug output a little
easier to read.
glsl: Properly pack GS output varyings

In geometry shaders, outputs are consumed at the time of a call to
EmitVertex() (as opposed to all other shader types, where outputs are
consumed when the shader exits).  Therefore, when packing geometry
shader output varyings using lower_packed_varyings, we need to do the
packing at the time of the EmitVertex() call.

This patch accomplishes that by adding a new visitor class,
lower_packed_varyings_gs_splicer, which is responsible for splicing
the varying packing code into place wherever EmitVertex() is found.
mesa/shaderapi: Allow 0 GEOMETRY_VERTICES_OUT.

ARB_geometry_shader4 spec Errors:
"The error INVALID_VALUE is generated by ProgramParameteriARB if <pname>
is GEOMETRY_VERTICES_OUT_ARB and <value> is negative."

Reviewed-by: Paul Berry <stereotype441@gmail.com>